1. Field of the Invention
The present invention relates to devices for fabricating liquid crystal display devices, and more particularly, to an inkjet printing device which forms an alignment film and the like of a liquid crystal display device.
2. Discussion of the Related Art
Super thin flat panel display devices, such as liquid crystal display devices which have a display screen thickness of a few centimeters, are used in a variety of applications including notebook computers, monitors, spacecrafts, airplanes. These flat panel display devices have low power consumption due to a low operating voltage and are portable, thus making them an attractive option for the above-mentioned applications.
In general, a liquid crystal display device includes a lower substrate and an upper substrate opposite the lower substrate where a predetermined gap separates the two and a liquid crystal layer formed between the two substrates. The liquid crystal layer changes an orientation of liquid crystals in the liquid crystal layer depending on a voltage applied thereto, thereby changing a transmittivity of light which enables image reproduction.
Since a desired image cannot be obtained if the liquid crystals in the liquid crystal layer do not properly orientate when a voltage is applied, an alignment film is formed on each of the lower substrate and the upper substrate which maintains an initial arrangement of the liquid crystals.
A rubbing alignment method or an optical alignment method may be used to form an alignment film.
In the rubbing alignment method, a thin film of alignment material is coated on a substrate, and a rubbing roll having a rubbing cloth wound thereon is rotated on the thin film, thereby arranging the alignment material on the thin film in one direction.
In the optical alignment method, a thin film of alignment material is coated on a substrate, a polarized or non-polarized UV beam is then directed onto the thin film of the alignment material. When the UV beam is directed onto the thin film, the alignment material reacts to the UV beam thereby arranging the alignment material in the thin film in one direction.
In order to obtain the alignment film arranged in one direction by applying the rubbing alignment or the optical alignment, a thin coat of the alignment material is uniformly applied on the substrate.
A related art method for coating an alignment material on a substrate will be described with reference to the attached drawings.
FIG. 1 illustrates a section showing a method for coating an alignment film by using a related art roll printing device.
The related art roll printing device contains a substrate stage 12 for supporting a substrate 10, and a dispenser 14 for supplying alignment material. The roll printing device includes a doctor roll 16, anilox roll 18, and a printing roll 20. The doctor roll 16 engages with the anilox roll 18 and the anilox roll 18 engages with the printing roll 20.
The printing roll 20 has a rubber plate 22 attached thereto suitable for printing a desired pattern of the alignment material.
A method for coating the alignment film using above roll printing device will be described. At first, alignment material 15 is dispensed between the doctor roll 16 and the anilox roll 18 with the dispenser 14. In this instance, because the doctor roll 16, the anilox roll 18, and the printing roll 20 are engaged with each other and rotate as shown in FIG. 1, the alignment material 15, supplied between the doctor roll 16 and the anilox roll 18, is evenly coated on the rubber plate 22 on the printing roll 20 by the anilox roll 18.
In the meantime, the substrate stage 12, having the substrate 10 placed thereon, moves in one direction under the printing roll 20. During the movement of the substrate stage 12, the substrate 10 on the substrate stage 12 and the rubber plate 22 on the printing roll 20 contact each other, such that the alignment material is transferred from the rubber plate 22 to the substrate 10, thereby coating the alignment material on the substrate 10.
However, the coating of the alignment material on the substrate by using such a roll printing device has the following drawbacks.
First, the sizes of the three rolls must be changed when a model size of the liquid crystal display device changes.
Second, for applications having a larger substrate which require a larger printing roll, it becomes more difficult to evenly coat alignment material on the entire surface of the substrate.
Third, use of the roll printing device wastes a fair amount of alignment material, thereby increasing production costs associated with coating a substrate using the related art roll printing device.
In response to these problems, an inkjet printing device has been used. A related art inkjet printing device, provided with an inkjet head having a plurality of nozzles for dispensing alignment material, dispenses the alignment material selectively from the plurality of nozzles. The related art inkjet printing device includes the flexibility of coating a variety of liquid crystal display devices having different sizes.
However, the related art inkjet printing device does not evenly coat alignment material when a portion of the alignment material is not fully discharged from the nozzle, but instead stays on the nozzle. In this instance, the nozzle may become clogged if a portion of the alignment material remaining on the nozzle sets.